1. Field of the Invention
This invention relates to an electronic system for controlling apparatus for peeling and coiling continuous strips of metal cut from a rotating work piece and more particularly, to an electronic system for providing continuous control of both strip thickness and coiling tension.
2. Description of the Prior Art
Machines have been built to manufacture thin metal strip by continuously feeding or moving a cutting tool at a predetermined rate into the peripheral surface of a rotating metal billet so as to cut and peel a continuous metal strip therefrom.
The prior art machines include a tension producing coiling assembly as part of the peeling process. As an example, the coiling assembly includes a motor driven rotatable spindle with a wrapping mechanism to start the wrap. The rotating spindle pulls and coils the metal strip as it is peeled from the billet. An example of such a machine is described in U.S. Pat. No. 3,460,366 and U.K. Pat. No. 1,522,507.
Prior art metal peeling machines have included electronic circuitry arranged to control the surface speed of the billet and the speed of the peeled strip since the surface speed of the billet and the speed of the strip are also factors determining strip thickness. However, prior art control circuits are not arranged to continuously monitor and regulate strip tension. This is a decided disadvantage if the strip tension varies during the peeling operation because of an abrupt change in the metallurgy of the billet, because of a change in coolant, or because of a build up on the tool rake surface.
Referring to FIG. 1, there is shown a simplified block diagram of a prior art electronic control system 10 for a peeling machine having a variable speed DC drive motor 11 arranged to simultaneously rotate a main spindle 12 and a lead screw 13. The main spindle 12 is adapted to provide a stable support for a billet 14 of material, such as metal. The lead screw 13 positions and drives a cutting tool 15 suitable for cutting the material of the billet 14. When the billet 14 is securely mounted on the spindle 12, the motor 11 is operated so as to rotate the spindle and the lead screw 13 in a preferred direction to feed or advance a cutting edge 16 on the cutting tool 15 into the surface of the rotating billet 14.
The rate of advancement of the cutting tool 15 or feed rate is controlled by a mechanical gear box 17 serially connected between the main spindle 12 and the lead screw 13. The mechanical gear box 17 is adapted to permit an operator to select one of several discrete feed rates suitable for a particular operation. A strip 18 is cut or peeled from the billet 14 when the billet surface is rotated against the cutting edge 16 of the cutting tool 15. The cut strip 18 is threaded beneath a first guard roller 19, through a pair of pinch rollers 20, and finally wrapped on a spindle 21 rotatably driven by another variable speed DC motor 22. Tension is applied to the strip 18 as it is being wrapped around the wind up spindle 21. The spindle 21 pulls the strip 18 as it rotates about its longitudinal axis and wraps the strip 18 around itself. The pulling force or tension applied to the strip 18 is an important factor determinative of the strip thickness.
It has been determined that the resultant strip thickness is not always equal to the depth of the cut or infeed of the cutting tool 15. During the cutting operation, the material ahead of the cutting tool 15 is plastically compressed causing a cut strip to "gather" up to two and one half times the thickness of the depth of cut. The ratio of the resultant strip thickness to the depth of cut is termed "gather ratio". The gather ratio is dependent upon the material being cut, the tool rake angle, the cutting speed, and the tension applied to the material being cut from the billet 14. Increasing the tension applied to the strip 18 lowers the gather ratio and the resultant thickness of the strip 18 by placing the strip material under tensile stress, thereby decreasing the plastic compression tendencies ahead of the cutting edge. Therefore, the greater the tension that is applied to the strip 18, the thinner the strip 18 becomes and the faster it travels. Conversely, lowering the tension decreases the tensile stress in the strip 18 and allows it to thicken and travel slower. Thus, the gather ratio is also the ratio of the surface speed of the billet, B.sub.ss, to the speed of the strip, LS. Gather ratio=billet surface speed/strip speed=strip thickness/feed rate.
In the prior art, electronic circuits are arranged to maintain a uniform strip thickness by controlling the ratio of the billet surface speed to the strip speed since the strip thickness is substantially equal to the product of the cutting tool feed rate multiplied by the gather ratio. In particular, the billet surface speed control circuit 23 includes a DC motor drive amplifier 24 having an output terminal 25 connected to a first terminal 26 of the main spindle motor 11. A second terminal 27 of the main spindle motor 11 is connected to ground potential 28. The amplifier 24 is adapted to amplify one or more input signals to provide an output signal, e.sub.3, suitable for operating the main spindle motor 11 at a desired speed. For convenience, the amplifier 24 is shown as a high gain operational amplifier with a feedback impedance 29 and first 30 and second 31 input impedances each having a terminal electrically connected to a common summing junction 32 and an inverting terminal 33 of the amplifier 24. A non-inverting terminal 34 of the amplifier 24 is coupled to ground potential 28 via a suitable conductive path 35. The input impedances 30,31, feedback impedance 29, and the conductive path to ground 34 are resistors, capacitors, or a combination of resistors and capacitors arranged as known in the art to provide a desired functional relationship between amplifier input impedance and amplifier output impedance.
Another terminal of the first input impedance 30 is connected to a movable contact 36 of a three terminal potentiometer 37 having a first fixed terminal 38 connected to ground potential 28 and a second fixed terminal 39 connected to a fixed amplitude, negative DC voltage, -V, from a source, not shown. The potentiometer 37 functions as an adjustable voltage divider for providing a negative DC input voltage, e.sub.1, to the amplifier, for setting billet surface speed. Another terminal 40 of the second input impedance 31 is connected to a movable contact 41 of a servo potentiometer 42 having a first fixed terminal 43 connected to ground potential 28. A second fixed terminal 44 of the servo potentiometer 42 is connected to a positive terminal 45 of a tachometer generator 46, which, in turn, is mechanically coupled to the main spindle 12 so as to generate a DC voltage having a magnitude proportional to the angular velocity of the main spindle 12. The movable contact 41 of the servo potentiometer 42 is driven and displaced by a suitable positional servo mechanism 47 coupled to the cutting tool 15. The servo potentiometer 42 functions as an adjustable voltage divider for providing a positive DC input signal, e.sub.2, to the amplifier 24 that varies in proportion to the position of the cutting tool 15 and the angular velocity or speed of the main spindle 12. The amplifier output signal, e.sub.3, applied to the main spindle motor 11 has a magnitude proportional to the difference in amplitude between the signal e.sub.1 and the signal e.sub.2. Consequently, the magnitude of the amplifier output signal, e.sub.3, varies in proportion to the position of the cutting tool 15 and the speed of the main spindle 12. Thus, as the cutting tool 15 is moved into the rotating billet 14 at a fixed feed rate selected by the gear box 17, the main spindle 12 and billet 14 are rotated by the motor 11 at a speed that increases in inverse proportion to the decreasing radius of the billet 14, whereby the surface speed of the billet, B.sub.ss, remains constant.
A control circuit 48 for the wind up spindle motor 22 includes a DC motor drive amplifier 49 such as a high gain operational amplifier having an output terminal 50 coupled to a first terminal 51 of the wind up spindle motor 22. A second terminal 52 of the motor 22 is connected to ground potential 28. The amplifier 22 includes a feedback impedance 53 connected between an amplifier inverting terminal 54 and the output terminal 50, an input impedance 55 with a terminal 56 connected to the inverting terminal 54, and a non-inverting terminal 57 of the amplifier 49 coupled to ground potential 28 via a suitable conductive path 58. The input impedance 55, feedback impedance 53, and the conductive path 58 are arranged as known in the art, to enable the amplifier 49 to operate in response to a DC voltage signal, e.sub.4, from a line speed regulating circuit 59. The voltage signal, e.sub.4, is applied to another terminal 60 of the input impedance 55 to enable the amplifier 49 to provide an output signal suitable for operating the motor 22 to rotate the spindle 21 and move the strip 18 through the rollers at a desired line speed.
The control circuit 59 for regulating the line speed of the strip 18 and establishing a fixed gather ratio or ratio of the billet surface speed to the strip speed includes a DC operational amplifier 61. An output terminal 62 of the amplifier 61 is coupled to the input impedance 55 of the amplifier 49 in the control circuit 48 for the wind up spindle motor 22. First 63 and second 64 gang tuned potentiometers each have a fixed terminal electrically connected to a common summing terminal 65 and an inverting terminal 66 of the amplifier 61. A movable contact 67 of the first potentiometer 63 is also electrically connected to the common summing terminal 65. A feedback impedance 68 is connected between the summing terminal 65 and the amplifier output terminal 62. A non-inverting terminal 69 of the amplifier 61 is coupled to ground potential 28 via a suitable conductive 70. A negative terminal 71 of a tachometer generator 72 is connected to a movable contact 73 and another fixed terminal 74 of the second potentiometer 64. A positive terminal 75 of the tachometer generator 72 is connected to ground potential 28. The tachometer generator 72 is mechanically coupled to one of the pinch rollers 20 so as to generate a DC voltage, e.sub.5, having a magnitude proportional to the speed of the moving strip 18. The movable contact 41 of the servo potentiometer 42 is connected to another fixed terminal 76 of the first potentiometer 63 for conducting the voltage signal, e.sub.2, proportional to the surface speed of the billet 14. Thus, the magnitude of the amplifier output signal, e.sub.4, coupled to the wind up spindle motor drive amplifier 49 is proportional to the difference in amplitude between the line speed voltage signal, e.sub.5, and the billet speed voltage signal, e.sub.2. The position of the movable contacts 67,73 of the first 63 and second 64 gang tuned potentiometers is varied to provide a desired gather ratio and an amplifier output voltage, e.sub.4.